Design of Experiments (DoE): A Step-by-Step Guide

Design of Experiments is a systematic method used to optimize processes, products, or systems by controlling and manipulating the input factors that influence the outcome that means you can determine the individual and interactive effects of various factors that can influence the output results of your measurements. Biostat Prime’s DoE allows researchers to evaluate multiple factors at the same time instead of relying on a one-factor-at-a-time experimentation approach.

DoE A Statistical Approach

DoE in statistical approaches tackle the complexity of controlled experiments by dealing with its planning, conducting, analyzes, and interpretation to assess the factors (i.e., input variables) that control the value of a parameter or group of parameters (i.e., response variables). The experiments allow the designers/researchers to analyze the effect of each input variable on the response variable and the effects of interactions between factors on the response variable. The design of the experiment and the analysis of obtained data are inseparable.

Basic Terminologies Used in Experimental Design

Experiment

An experiment is a systematic procedure carried out with the goal of investigating, testing, or validating a hypothesis, theory, or scientific question and finding the final answer.

Treatment

The individuals, groups, objects, or processes which are to be compared in an experiment are called treatments. Treatments are manipulated by researchers to observe how they influence the response variable, allowing for the investigation of cause-and-effect relationships.

Factor

Also known as input variable or categorical variable is the independent variables in an experiment that a researcher or experimenter can change or control during an experiment to observe its effect on the response variable. Factors represent the different conditions or levels under which the experiment is conducted, and the systematic variation of factors allows us to understand how the changes in these variables influence the outcome of the experiment.

Factor Level

A factor can have different levels which represent different variations or conditions of the factors that are systematically tested in the experiment.

Experimental Unit

It is the smallest and most basic element of experimental design which is randomly assigned to treatment. The choice of experimental units depends on the nature of the study and the research question being addressed.

Principle of Design of Experiment (DOE)

The principles of Design of Experiments (DOE) provide a systematic and structured approach to planning, conducting, and analyzing experiments and helps the researchers in efficiently understanding the effects of multiple factors on a response variable to identify the most influential factors with the least number of experimental trials.

Randomization

The principle of randomization involves randomly assigning experimental units to different treatments or conditions. Randomization helps controlling potential biases and distributing the unknown variation due to confounded variables. Without random assignment, there is a risk that differences in outcomes between groups could be attributed to factors other than the treatment itself.

Replication

Replication involves repeating treatments under the same conditions to increase the number of observations and with the increase in number of observations the precision of experiment increases. Replication helps assess the variability in the results thus improves the reliability of research findings. It allows researchers to estimate experimental error and enhances the statistical validity of the experiment.

Blocking

Blocking involves grouping experimental units based on known sources of variability that could affect the results. By blocking, researchers can control these sources of variation and ensure that comparisons are made within similar subsets of experimental units. This is particularly useful in situations where there are identifiable patterns of variability.

How to Design an Experiment

  1. Define the Problem and objective of the experiment and identify the response variable that you want to measure.
  2. Identify the input variables (independent variables or factors) that may influence the response.
  3. Determine the different levels for each factor. Levels represent the specific values or settings that the factors can take during the experiment.
  4. Choose an appropriate experimental design (e.g., Full Factorial, Fractional Factorial, Taguchi Method).
  5. Randomize the order of experimental units.
  6. To improve the reliability of the result, include the replication of experimental runs.
  7. If there are known sources of variability that could affect the results, consider blocking or grouping experimental runs accordingly.
  8. Conduct the experiments and collect the data systematically and ensure the measurements are accurate.
  9. Use statistical methods (ANOVA, regression analysis) to analyze the data and identify significant factors and interactions.
  10. Based on the analysis, optimize the process or system by adjusting the levels of significant factors.
  11. Confirm the results through additional experiments or validation studies and document the experimental design, procedures, results, and conclusions for future reference.